North-facing rooms receive indirect, relatively cool and consistent daylight with no direct sun — colours can read flatter and cooler than in a sample book or a well-lit shop.
Hemisphere note: This describes typical Northern Hemisphere daylight. In the Southern Hemisphere, north-facing rooms typically get the strong, warm direct sun described here for south-facing rooms — the physical mechanism is the same, but which compass direction gets the sun is reversed.
Warm-undertone colours generally cope better, since they counteract rather than compound the room's cool, flat light.
Cool greys and blues can look noticeably flatter or greyer than expected — a colour that looked crisp in a bright shop can look dull once painted.
Testing advice
Test a physical sample on the actual wall and view it at different times of day, including overcast conditions, before committing.
Lighting simulations and descriptions here are approximations, not exact physical predictions — see methodology.